Instrumented bearings comprise a bearing and a sensor unit for sensing the angular position of a rotatable ring of the bearing with respect to the fixed ring. Such sensor units often include an encoder element, adapted to generate magnetic field variations, and a sensing element adapted to determine, on the basis of the magnetic field variations, the angular position of the rotatable ring. The sensing element is generally fixed with respect to the fixed ring of the bearing, thanks to a casing in which the sensing element is mounted.
To guarantee an accurate magnetic detection and an accurate rotation speed sensing, it is compulsory that the sensing element is accurately mounted on the bearing. It is known from EP-A-1 431 071 to mount a tubular snap portion of a sensor casing in a groove realized on a surface of the fixed ring of the bearing. As such a groove is generally obtained thanks to a turning operation, it offers a relatively low dimensional accuracy along its central axis. The mounting accuracy of the casing is therefore not satisfying.